The invention relates to a testing method for defining the properties of moulding material systems in casting works and their components by measuring the elastic and non-elastic properties (propagation and absorption of elastic waves) by means of ultrasound, incorporating further physical and/or technical-technological characteristic values. The ease with which the measurements are made by way of this testing method (no destruction, speed, possibility of automation) permits new testing systems to be developed for testing the moulding material and also for monitoring and controlling quality in the preparation and manufacture of the mould and core.
Further, the present invention relates to an apparatus for finding out the characteristics of casting works moulding sand, in particular for defining the properties and/or composition of casting works moulding sand, having a sample-taking device and a test sleeve which receives a sample of moulding sand, preferably in the form of a precompacted testing body.
The properties in respect of the processing technology of a moulding material are representative of a combination of material-related factors, technological factors and equipment-related factors, each of which have an influence on the preparation-, moulding- and/or casting process. The moulding material composition--moulding material quality--moulding quality chain purposefully influences the quality of the cast article. To that end, testing characteristic values are involved which have a direct influence on changes in the material with effects on the moulding technology related properties.
The conventional method of testing moulding materials often places the quality of the material under conditions which are close to practice. A relatively large amount of time is involved which restricts the "sensitivity of the reaction" to disturbance magnitudes, and the meaningfulness of statements made about it is likely to be deficient.
Methods in applied physics which have developed on the principle of advanced measuring technology enable a detailed definition to be made of the physical properties and their relationship, above all, to active physical and also technical-technological parameters. Taking into consideration the conditions specific to casting, such processes can be used for practical implementation of moulding material testing and moulding material controlling methods, and they have considerable advantages over conventional testing processes (e.g. possibilities for automatic realisation, greatly reduced testing times, inter alia). This makes itself very apparent when moisture is measured in clay bonded moulding materials by way of an electromagnetic process, or when the hardening condition is measured during manufacture of the core by way of an electric process.
Moulding technology-related properties of clay bonded moulding materials are mainly defined by measuring compressibility and compression strength, wherein these values are, in turn, dependent on water content, granulometric characteristic values (sludge content) and bindable proportion of clay (active clay). The most customary processes for defining these characteristic values are the processes used in many casting works in the form of analyses made of the sieve, sedimentation and adsorption. Such testing methods are suitable enough, but they are costly, particularly in terms of time, and they cannot be automated or used with attendant monitoring of the process. With previously known automatic systems for controlling optimum moulding material properties, measurements are taken of the compressibility and water content, of the compression strength and shearing strength or deformation limit. These measurements, with the exception of that for defining water content, are taken after the moulding material has been mixed, and on the basis of these measurements the measured amounts of clay and water are worked out for the following mixing charge. One drawback with systems such as this is that no consideration is taken, or insufficient consideration is taken, of fluctuations in the sludge part and in the active clay part which occur during operation, since the measured amounts for the current mixing charge are calculated from the measured values of previous charges. To overcome this problem, process data is used (e.g. sand/casting ratio and amount of core placed in the mould). However, associating this data with the individual mixing charges is unreliable (e.g. discharge of core sand from the circulation of moulding material, infiltration of old casting works sands during transportation), which means that in practice the values to be worked with are inaccurate, and this naturally has an unfavourable effect on the success of controlling the operation.
One possible solution which provides for attendant definition of the quality of old casting works sand is disclosed in DD-PS 253197. This proposes a process for on-line definition of the water-, sludge- and active clay content in the old sand of the casting works, wherein the attenuation of Rontgen- or gamma radiation and ultrasonic speed are determined on samples of moulding material. Transposition of this measuring concept fails because of the increased technical requirements imposed on the radiometric measurement operation (safety requirements, maintenance costs).
In controlling uniformity and quality of organic binding agents and of water glass bonded moulding materials, the mechanical properties of the testing bodies for such moulding material mixtures are defined. It is mainly a question of testing bending strength, but also other measurements of strength are involved (e.g. shearing strength and compression strength). Also, rheological properties are examined (e.g. deformation testing, duration of processability) of the moulding material mixes. Since defining the strength obtainable through hardening is a fundamental criterion for the quality of the moulding material, a hardening feature is usually determined, wherein the strength obtained is represented in dependency on the duration of the hardening process. In sito measurements using these testing methods are not possible. Automation or on-line execution of monitoring and controlling operations is undesirable, or are not possible, because of the cost.
DE-PS 3152073 discloses one proposal for carrying out attendant definition and control of the quality of the core sand. According to this proposal, the necessary hardening time is calculated by measuring the magnitude of electrical conductivity on a testing body before and after it hardens, and the variation range of that magnitude is simultaneously defined. The magnitude of electrical conductivity corresponds to a hardness degree for the core which is such that it ensures that the core attains previously set down strength properties, and is thus used as a yardstick for controlling core quality. One drawback with this method should be mentioned, namely the lack of flexibility in assessing the electrophysical properties with a view to application to other moulding material systems.
At present, in order to assess the effect of regeneration, reference is made exclusively to the characteristic values of old sand in casting works: "washable substance" and "loss on ignition". The testing methods for defining these characteristic values are known from conventional testing of clay bonded moulding materials, and they have all the advantages and disadvantages of those measuring processes, see above.
Apparatus of the above mentioned kind which is already highly automated in many instances is in widespread use in casting works. Therein, a cylindrical test sleeve which is open at both ends, but which is initially without application of pressure, is filled with moulding sand. To this end, the open underside of the test sleeve is, at least temporarily, closed by a pressure plate or the like. The sleeve which is filled in this way is then conveyed to a compressing station where a stamp is pressed down onto the moulding sand from the open top side of the test sleeve, and compresses the mouldlng sand. By measuring the path which the pressure stamp covers In the test sleeve when this takes place, it is possible to define the compressibility of the moulding sand.
In another station it is possible to measure the shearing strength of the compressed testing body, by the testing body being pressed out of the sleeve by the pressure stamp or another stamp, for example, after the pressure plate which initially closes the sleeve has been removed, or after the test sleeve with the testing body has been taken from the pressure plate. The part of the testing body projecting from the test sleeve can then be sheared off by a laterally attacking fork, wherein the forces which act upon the fork are measured. In addition to measuring the shearing strength, further automatic measuring stations can be provided, for example for defining moisture and other parameters with the aid of various sensors and including contact-free measuring methods or measuring methods which operate by making contact.
However, some of the measuring- and investigational methods are relatively costly, particularly if indications are to be given on the composition of the moulding sand, with the content of active bentonite and sludges being the main interest. The content of active bentonite and of sludges has a considerable influence upon the moulding technological properties of the moulding sand. Therefore, there is a need for an apparatus which makes it possible to define, in a quicker and simpler manner, the properties of the moulding sand which are important for purposeful application.